Antibacterial mechanisms of Zataria multiflora Boiss. essential oil against Lactobacillus curvatus

- GC-FID analysis revealed carvacrol and thymol as main components of ZMEO.
- Antibacterial activity of ZMEO against L. curvatus was evaluated.
- Mechanism of antibacterial action of ZMEO against L. curvatus was evaluated.
- The ZMEO affected membrane permeability and cell integrity of L. curvatus.
- Morphological changes in the bacterial cells were confirmed by TEM observations.

The chemical composition of ZMEO was analyzed by GC-FID, and consequently 14 components were identified. Carvacrol (39.29%) and thymol (25.24%) were found to be the major components. The diameter of inhibition zone (2.68 cm), minimum inhibitory concentration (6.6 μl/mL), and minimum bactericidal concentration (9.10 μL/ml) of ZMEO against L. curvatus was evaluated. To determine antibacterial mechanisms of ZMEO against L. curvatus the cell permeability, membrane integrity and membrane potential changes and cell microstructure were determined. When ZMEO was added at 2 × MIC levels, the number of cells decreased significantly from 5.45 to 1.34 log10 CFU/mL over 24 h of incubation. The REC of the treated samples increased after the addition of ZMEO at MIC and 2 × MIC. In addition, the ZMEO revealed its mode of action on membrane integrity as confirmed by loss of 260-nm absorbing materials. After 0, 30, 60 and 120 min of exposure time, concentration of cell constituents in suspensions treated with MIC essential oil increased by 1.44, 4.16,11.94 and 16.11 times, while they increased by 2.11, 11.72, 18.77 and 20.77 times when treated at 2 × MIC. The TEM analysis showed the inhibitory effect of ZMEO as confirmed by considerable morphological alterations on the cell wall L. curvatus.